This invention relates to crushing machines for crushing aggregate and the like; and in particular to mobile crushing machines such as are used in quarries or for recycling demolition waste.
One type of crushing machine uses a crusher. A cone crusher has a pair of frusta-conical members arranged with their apexes upwards, and with an annular gap between them that decreases in width from top to bottom. The inner cone is rotatable relative to the outer cone on an eccentric, so that material fed in at the top is crushed between the cones as the gap varies, and then falls out at the bottom. Cone crushers are efficient at crushing various types of material, such as rock or stone, to a given size. However, it is important to ensure that no metal is fed into the crusher, since this can cause extensive damage to the cones. It is known to address this problem by providing a metal detector on a conveyor feeding the material to the crusher, so that the machine operator can then stop the conveyor, find the metal in the material by hand, remove it and then restart the conveyor. This is time-consuming, and not a pleasant task for the operator.